1. Field of the Invention
The present invention relates to an optical information recording medium, and more particularly to an optical information recording medium comprising a recording layer which comprises a composition of antimony, sulfur, and one element selected from the group consisting of the elements belonging to group IIB and group IVA of the periodic table.
2. Discussion of the Background
As the demand for recording large volumes of information signals on a recording medium at a high recording density is increasing, many kinds of information recording media have been proposed on the basis of various configurations and operation principles, and information signals are thus recorded therein at a high density and reproduced therefrom.
There are conventionally many kinds of recording methods using the abovementioned information recording media. For instance;
(1) Information signals are recorded on an information recording medium in such a fashion that pits or dents are formed on a thin recording layer which is overlaid on a substrate of the information recording medium by the application of a recording beam, for which the intensity is modulated in accordance with the information signals, to the recording side of the abovementioned recording medium.
(2) Information signals are recorded on an information recording medium in such a fashion that an optical constant such as the refractive index of a thin recording film which is overlaid on a substrate of the information recording medium is changed by the application of a recording beam, for which the intensity is modulated in accordance with the information signals, to the recording side of the above-mentioned recording medium.
(3) Information signals are recorded on a magneto-optical recording medium in such a fashion that the magnetized direction of a thin recording film which is overlaid on a substrate of the magneto-optical recording medium is changed by the application of a recording beam, for which the intensity is modulated in accordance with the information signals, to the recording side of the above-mentioned recording medium.
Furthermore, to reproduce the information signal from the above-mentioned recording media, a laser beam with a predetermined intensity is applied to the recording media.
The aforementioned information recording methods have their own shortcomings.
The recording method (1) has the shortcoming that the reproduction C/N ratio is degraded when the pits or dents which are formed on the thin recording layer are deformed. In addition to the above, a protective layer cannot be overlaid on the thin recording layer.
In the recording method (2IVA), the phase of the recording layer is caused to change by the application of the laser beam thereto. According to this method, the information can be recorded on the medium and reproduced therefrom on the principle that the refractive index of the recording layer varies depending on its phase. For the material of this kind of recording layer, Te-Ge compounds, In-Se compounds, Sb-Se compounds and Se-Te compounds are generally used. When the above-mentioned compounds are used for the recording layer, a laser beam having an intensity of as great as 10 mW or more is required to change the recording layer from the amorphous phase to the crystalline phase. Furthermore, the phase change from the amorphous phase to the crystalline phase proceeds slowly because of the slow rate of the crystallization in the compound, so that information cannot be recorded on the medium and reproduced therefrom at high speed.
In the recording method (3), it is difficult to obtain an adequate C/N ratio because the reproduction output is small.